Torsional dampers are a vibration-absorbing device used in a flywheel, a clutch disc, or a driving system to absorb torque variations of a combustion engine or an electric motor (Patent Documents 1 and 2).
Such a torsional damper is freely fitted into a coil spring arranged in the direction of relative rotation as an elastic means disposed between a driving plate connected to a driving source and a driven plate coupled to a driven source.
The torsional damper is an approximately cylindrical cushion formed of a composite comprising a resin material and a rubber material.
When the relative rotation of a driving plate and a hub exceeds a predetermined value due to a sudden torque change between an engine and a input shaft caused by a shift change of a vehicle or a sudden increase in torque generated by a driving source, a torsional damper is compressively deformed together with a coil spring, reduces impact torque by the elasticity of the torsional damper, and at the same time, prevents buffer wear of the spring coil when the coil is compressed.
Patent Document 3 discloses a specific EPDM (ethylene propylene diene rubber) composition as a rubber material used for torsional dampers.